1. Field of the Invention
The present invention relates to an inspection of a semiconductor device in a manufacturing process, and more particularly to a semiconductor device inspecting apparatus for judging whether a semiconductor device is good or bad by measuring a current which flows in such a way that it compensates for a secondary emission caused by electron beams which have passed through contact holes and reached a substrate when the semiconductor device in a manufacturing process is irradiated with the electron beams.
2. Related Background Art
There are the following known examples of techniques for measuring a current, which flows in such a way that it compensates for a secondary emission caused by electron beams, which have passed a contact hole and reached a substrate when the semiconductor device in a manufacturing process is irradiated with the electron beams. In Application Ser. No. 09/057,455, there is disclosed detecting a current caused by electron beams which have passed through a contact hole and reached a substrate and detecting a position or a size of a bottom of the contact hole as shown in FIG. 1 and FIG. 2. In addition, in Application Ser. No. 09/451,440, as shown in FIG. 3, there is disclosed irradiating an area including a plurality of contact holes with electron beams and measuring compensation current values on the substrate generated by the electron beams passing through the contact holes to check the ratio of normal contact holes in the area. Furthermore, in Application Ser. No. 09/702,831, as shown in FIG. 4, there is disclosed an inspection method for determining a good or bad product by measuring waveforms of different chips and comparing them with a reference value by a subtraction. Still further, as shown in FIG. 5, there is shown a method of extracting an extrapolating D.C. component by irradiating repeatedly with electron beams in different scanning frequencies and measuring current waveforms in order to remove capacitance components generated by electron beam scanning. In Application Ser. No. 09/722,074, as shown in FIG. 6, there is disclosed a method of making etching conditions by comparing measured compensation currents using trial samples formed under different etching conditions.
In the prior arts set forth hereinabove, the current generated by electron beams applied to an object to be measured is used as compensation current generated by directly irradiating a semiconductor substrate at the bottom of the contact holes. While a measured current value is minute from the beginning as a picoampere or lower, a microstructure and a high precision are accelerated in a measured portion, thereby causing a demand for a further improvement of a measurement precision. In addition, the current value measured is minutely a picoampere or lower as described in the above and therefore there is a defect of a current variation caused by an effect of a stray capacitance according to measuring conditions or measuring equipment. Furthermore, an electron beam source is designed so as to operate very stably as measuring equipment, by which a variation per day is only 1% or so, which is not a problem in a normal usage. If, however, contact holes condition is checked by electron beam scanning, the current variation itself is about 1% and therefore an error occurs in a measurement value of the compensation current only by a weak fluctuation of the electron beam current. As causes of the beam current fluctuation, there can be a temperature change of the beam source, deterioration with age of the beam source, a variation of power supplied to the beam source. Furthermore, there is a problem that the obtainable waveform requires much time to enter a steady state since an LCR value depends upon an apparatus or a wafer and therefore it takes much time for an analysis of whether the measurement value can be adopted. Besides, for determining whether an apparatus is normally operating or whether the measured waveform is reliable, the determination is difficult in some cases only by a waveform measured once.
An object of the present invention is to solve these problems and to provide a semiconductor device inspecting method that enables a high-precision nondestructive inspection with a reduction of external noises.
The prior arts set forth hereinabove are basically for measuring a current which flows in such a way that it compensates for a secondary emission caused by an irradiation with electron beams. Therefore, the measured current value is minutely a picoampere or lower, by which the measurement value may be affected by measuring conditions, a structure or material of a semiconductor device to be measured, or a time constant of measuring equipment.
It is an object of the present invention to solve this problem and to provide a semiconductor device inspecting apparatus capable of a high-precision nondestructive inspection with a reduction of external noises.
According to a first aspect of the present invention, there is provided a semiconductor device inspecting apparatus, comprising: an electron gun for irradiating a area on a sample with electron beams to be inspected where a semiconductor device is formed, an electron beam control section for controlling these electron beams, current measuring equipment for measuring compensation current of secondary electrons generated by electron beams which have passed through contact holes in the inspected area and reached an underlying conductive layer, a data processor for determining a reference for judging whether an inspected area is good or bad, which is a current value obtained by using the current measuring equipment when irradiating an area having one or more contact holes treated as the inspected area sequentially or collectively with electron beams, and a storage device for storing the data processing result, wherein the storage device stores a background value, which is a current value obtained when irradiating an area made of the same material and having the same structure except that it has no contact hole in the same sample as the area having the contact holes in the inspected area and the data processor performs data processing of subtracting the background value stored in the storage device from the current value obtained by using the current measuring equipment when irradiating the area having one or more contact holes treated as the inspected area. Therefore, there is provided a semiconductor device inspecting apparatus, comprising: an electron gun for irradiating a area on a sample with electron beams to be inspected where a semiconductor device is formed, an electron beam control section for controlling these electron beams, current measuring equipment for measuring compensation current of secondary electrons generated by electron beams having reached an underlying conductive layer in the inspected area, a data processor for determining a reference for judging whether an inspected area is good or bad, which is a current value obtained by using the current measuring equipment when irradiating an area having one or more contact holes treated as the inspected area sequentially or collectively with electron beams, and a storage device for storing the data processing result, wherein the storage device stores the current value of the electron beams having reached the inspected area from the electron gun emitting the electron beams after a beam measurement with a detector and the data processor corrects the current value obtained by using the current measuring equipment when irradiating the area having one or more contact holes treated as an inspected area sequentially or collectively with electron beams on the basis of the measurement value of the beam measurement. It is effective if there is a relatively small difference between the current value of an area where the contact holes are formed and the current value of the area where no contact hole is formed such as a case of an extremely small contact hole density of the area to be inspected depending upon a thickness or a type of an insulating film, thereby enabling a calculation of compensation current flowing in the semiconductor substrate from which the background value is subtracted.
According to a second aspect of the present invention, there is provided a semiconductor device inspecting apparatus, comprising: an electron gun for irradiating a area on a sample with electron beams to be inspected where a semiconductor device is formed, current measuring equipment for measuring compensation current of secondary electrons generated by electron beams having reached an underlying conductive layer in the inspected area, a data processor for determining a reference for judging whether an inspected area is good or bad, which is a current value obtained by using the current measuring equipment when irradiating an area having one or more contact holes treated as the inspected area sequentially or collectively with electron beams, and a storage device for storing the data processing result, wherein the current measuring equipment has a first current/voltage exchanger connected to electrodes on which the sample is placed, a second current/voltage exchanger connected to opposite electrodes arranged in the vicinity of the sample to be inspected, and a differential amplifier for determining a difference between a measurement value of the first current/voltage exchanger and a measurement value of the second current/voltage exchanger and wherein the differential amplifier is connected to the data processor. According to this constitution, the opposite electrodes are capable of canceling an effect of a stray capacitance, by which a microcurrent can be measured.
According to a third aspect of the present invention, there is provided a semiconductor device inspecting apparatus, comprising: an electron gun for irradiating a area on a sample with electron beams to be inspected where a semiconductor device is formed, an electron beam control section for controlling these electron beams, current measuring equipment for measuring compensation current of secondary electrons generated by electron beams having reached an underlying conductive layer in the inspected area, a data processor for determining a reference for judging whether an inspected area is good or bad, which is a current value obtained by using the current measuring equipment when irradiating an area having one or more contact holes treated as the inspected area sequentially or collectively with electron beams, and a storage device for storing the data processing result, wherein the data processor compares a current waveform obtained by using the current measuring equipment with a standard waveform previously stored in the storage device as a standard waveform when irradiating the predetermined area having one or more contact holes on the semiconductor device with electron beams by using the electron gun and, if the comparison result exceeds the predetermined range, determines whether it is caused by a defect of the inspected area or of the inspecting apparatus. According to this constitution, it is possible to determine automatically whether the excess is caused by a defect of the inspecting apparatus such as an abnormality of the current/voltage exchanger easy to oscillate due to high amplitude or by an abnormality of the inspected area of the semiconductor device.
In addition, the standard waveform has a transient waveform pattern including overshoots at a rising edge and a falling edge of the waveform and a damped oscillation which follows thereafter; if the comparison result exceeds a predetermined range, it is determined to be an abnormality of the inspecting apparatus, and if the comparison result is within the predetermined range, it is determined to be an abnormality of the semiconductor device to be inspected. The data processor may include a data processor, which determines a defect of the device when the comparison result exceeds the predetermined range. In this condition, the comparison means makes a comparison in one or more of the rise time, an overshoot amount, an overshoot period, a flat period, an undershoot amount, an undershoot period, a zero-point offset, and a frequency analysis value of the waveform.
According to a fourth aspect of the present invention, there is provided a semiconductor device inspecting apparatus, comprising: an electron gun for irradiating a area on a sample with electron beams to be inspected where a semiconductor device is formed, an electron beam control section for controlling these electron beams, current measuring equipment for measuring compensation current of secondary electrons generated by electron beams having reached an underlying conductive layer in the inspected area, a data processor for determining a reference for judging whether an inspected area is good or bad, which is a current value obtained by using the current measuring equipment when irradiating an area having one or more contact holes treated as the inspected area sequentially or collectively with electron beams, and a storage device for storing the data processing result, wherein the storage device stores a current value of the electron beams having reached the inspected area from the electron gun for irradiating the electron beams by using a detector for a beam measurement of the current value and the data processor corrects the current value obtained by using the current measuring equipment when irradiating an area having one or more contact holes treated as the inspected area sequentially or collectively with electron beams on the basis of the measurement value of the beam measurement. Therefore, even if the electron beams fluctuate due to a temperature change of the beam source, deterioration with age of the beam source, a variation of power supplied to the beam source, the detector measures the beams and corrects the measured current, by which an accurate measurement value is obtained.
Preferably the detector includes a detector such as, for example, a Faraday cup, arranged in an electron beam irradiation position instead of a sample to be inspected at one or more of the time points before, during, and after the inspection of the sample to be inspected or before, during, or after the inspection of an individual inspected area on the sample to be inspected.
According to a fifth aspect of the present invention, there is provided a semiconductor device inspecting apparatus, comprising: an electron gun for irradiating a area on a sample with electron beams to be inspected where a semiconductor device is formed, an electron beam control section for controlling these electron beams, current measuring equipment for measuring compensation current of secondary electrons generated by electron beams having reached an underlying conductive layer in the inspected area, a data processor for determining a reference for judging whether an inspected area is good or bad, which is a current value obtained by using the current measuring equipment when irradiating an area having one or more contact holes treated as the inspected area sequentially or collectively with electron beams, and a storage device for storing the data processing result, wherein the data processor reads and processes a current value in an area where the current is stabilized after the irradiation with the electron beams among measurement values obtained by using the current measuring equipment. Even if an LCR value of the obtainable waveform depends upon an apparatus or a wafer, an area in which the waveform is in the steady state is previously stored and the current value is read in the stabilized area, thereby preventing a time loss caused by re-measurement.
For an inspection of the same sample to be inspected in another inspected area or of another sample of the same type to be inspected, the apparatus preferably includes means for reading the current value after an elapse of a waiting time stored in the storage means after the irradiation with the electron beams.